Process for producing a layered material in sheet or membrane form from thermoplastic foam

ABSTRACT

A process for producing a layered material in sheet or membrane form from thermoplastic foam is described. The laminated material is suitable in particular for use as a drainage sheet or membrane. To produce the membrane, the thermoplastic foam in the form of strips, lengths, shreds or the like is piled up to form a layer of uniform height and compressed and compacted at a temperature below the softening temperature of the foam. Subsequently, the compressed and compacted layer of thermoplastic foam is perforated and fused with the aid of pins which are heated to a temperature of 400° to 800° C., whereupon the perforated and fused layer is cooled while maintaining the compression.

FIELD OF THE INVENTION

The invention relates to a process for producing a laminated material insheet or membrane form from thermoplastic foam, in particular for use asa drainage sheet or membrane.

Prior Art

A process of the generic type is known from DE-C2-30 37 011(US-A-4,417,932). According to this process, membranes or sheets areproduced from remnant shreds of polyethylene foam of high apparentdensity by means of radiant heat and subsequent pressure treatment. Adisadvantage of the known process is the high expenditure on apparatus.Furthermore, this process is suitable only for the processing of foamshreds of uniform apparent density. High fault susceptibility is to beobserved in particular in the case of low apparent densities (less than80 kg/m³).

Similar processes are also known from British Patent 1,578,045 andUS-A-3,746,610.

Object

The object of the present invention is, therefore, to provide a processfor producing a layered material in sheet or membrane form fromthermoplastic foam, in particular for use as a drainage sheet ormembrane, which makes it possible to process foam material of variousapparent densities with low expenditure on apparatus.

SUMMARY OF THE INVENTION

This object is achieved according to the invention by

the thermoplastic foam in the form of strips, lengths, shreds or thelike being piled up to form a layer of uniform height and

being compressed and compacted at a temperature below the softeningtemperature of the foam,

by the compressed and compacted layer of thermoplastic foam beingperforated and fused with the aid of pins, which are heated to atemperature of more than 250° C., preferably up to 800° C. (e.g., 400°to 800° C.), and which have an outside diameter of 2 to 15 mm, at anaverage spacing of 10 to 50 mm and with a dwell time of the pins of 1 to10 s

and by the perforated and fused layer subsequently being cooled whilemaintaining the compression.

An essential feature of the invention is that the compacted foam strips,lengths or shreds are fused to one another within a short time by meansof heated metal pins or the like. The high maximum temperature of thepins, preferably 600° to 700° C., has the effect that the foam materialis in contact with the metal pins only for a short time and issubsequently further heated indirectly, i.e., by thermal conduction orthermal radiation. Accordingly, the finished membrane or sheetsubsequently has perforations composed of channels, the individualchannels having a diameter which is approximately 2 to 4 mm greater thanthe diameter of the pins used.

The process according to the invention can be performed bothdiscontinuously and (quasi) continuously. In the case of a discontinuousprocedure, for example, foam shreds of chemically or physicallycrosslinked polyethylene foam, in particular remnant or recyclingmaterial, are poured into a mould, the filling height preferably being20 to 200 mm, especially 30 to 150 mm. If a foam material of highrelative density is used, a low filling height is preferred and, if foammaterial of lower relative density is used, a higher filling height ispreferred. The mould is subsequently closed by means of a perforatedcover and the foam is compressed. Subsequently, externally heated orinternally heatable metal pins are pushed through the holes of the coverand, after a dwell time of 1 to 10 s, preferably 2 to 4 s, are withdrawnagain. The heated or heatable metal pins may in this case be arranged inone or more rows, if appropriate all the holes or channels may also beproduced simultaneously by a correspondingly high number of metal pins.The diameters of the holes of the cover are expediently adapted to theoutside diameter of the heated or heatable metal pins.

The process according to the invention can be carried out (quasi)continuously in a particularly cost-effective way by shreds or the likeof thermoplastic foam, preferably of chemically or physicallycrosslinked polyethylene foam, being compacted between twocompression-resistant chain belts (double-belt press) and fed to afusing station. The compression-resistant chain belts are, in this case,expediently perforated and move in steps. During the standstill phase,the fusing is performed by pushing externally heated or internallyheated metal pins through the perforations of the belts in rows orgroups. In a following cooling zone, the compression is maintained bythe belts. For smoothing the surface, a thin membrane of foam or plasticmay be drawn in at the same time. If appropriate, after leaving thechain belts, the surface of the membrane of shreds may be heated bymeans of hot air and smoothed by cold rolls. Finally, edge trimming canbe carried out, and this is expediently performed in line.

A major advantage of the process according to the invention is thatrecycling foam material containing fibrous material can also be used.Furthermore, foam material of various densities can be used, includingin mixtures.

BRIEF DESCRIPTION OF THE DRAWING

The process according to the invention is described in further detailbelow with reference to the drawing, in which:

FIG. 1 shows a basic diagram of an installation for the continuousproduction of a drainage membrane.

DETAILED DESCRIPTION EXAMPLE 1

For the (quasi) continuous production of a drainage membrane of athickness of 20 mm, foam shreds of an average dimension of 25 mm and anaverage apparent density of 80 kg/m³ are introduced by means ofconveying devices (not shown) into the metering hopper 1. The meteringroll 2 controls the conveying rate of the foam shreds by means of acontrol device (not shown).

The foam shreds are subsequently conveyed by the lower chain belt 3 atroom temperature into the wedge-shaped gap 5 between the lower chainbelt 3 and the upper chain belt 4 and elastically compressed between thechain belts 3, 4 to a thickness of 18 mm.

In the illustrative embodiment shown, the useful width of the chainbelts is 500 mm. The individual plate-shaped chain links have a width of100 mm each; correspondingly, the stepped advancement of the chain beltsis likewise 100 mm. Each plate-shaped chain link has in each of 5 rows25 holes of a diameter of 8 mm and a mutual center-to-center spacing of20 mm (not shown in the figure).

The stepped advancement of the chain belts 3, 4 is performedsynchronously by the advancing device 8, an exactly coordinatedplacement of the holes of the two chain belts 3, 4 being brought aboutby the synchronizing means 9, for example, in the form of preciselyaligned cams on the chain belts.

In every standstill phase of the chain belts 3, 4, a lifting means 7,provided with 5×25 heating pins 6, is actuated, the individual heatingpins, of a diameter of 4 mm and an initial surface temperature of 650°C., being pushed through the upper chain belt 4, the layer of foamshreds, compacted in the cold state, as well as through the lower chainbelt 3. The dwell time of the pins in the layer of foam shreds is 3 s.In this time, the foam shreds are partially melted and fused to oneanother by thermal conduction and radiation. After each "fusingoperation", the metal pins 6 are withdrawn from the two chain belts andthe layer of foam shreds lying inbetween, so that the next steppedadvancement of the chain belts by 100 mm can be performed.

The pressure of the chain belts 3, 4 at a level of about 1.5 bar ismaintained substantially constantly up to the chain deflection points10, 11. As a result, the layer of foam shreds can cool and themechanical compaction can be fixed. In addition, the bonds produced bymeans of heat receive their mechanical strength by cooling beforeleaving the compression zone. For edge limitation, usual limitationelements (not shown) may run along between the chain belts.

After leaving the cooling zone, the finished membrane of a thickness of20 mm and an average relative density of 140 kg/m³ is made up into rollor sheet stock in a known way by longitudinal and transverse cuttingapparatuses.

EXAMPLE 2 to 4

The same procedure as in Example 1 is followed, only the composition ofthe foam shreds having been varied, as follows:

    ______________________________________                                              Average piece                                                                             Apparent density                                                                           Apparent density                               Exam- size of the of the shreds                                                                              of the drainage                                ple   shreds (mm) (kg/m.sup.3) membrane (kg/m.sup.3)                          ______________________________________                                        2     30 × 30 × 10                                                                  30             120                                          3     30 × 30 × 7                                                                   140            187                                          4     30 × 30 × 4*                                                                  125     (75%)  196                                                30 × 30 × 10                                                                  30      (25%)                                               ______________________________________                                         *With nonwoven lamination                                                

The finished membranes or sheets of adequate strength and flexibilityhave perforations right through for drainage purposes corresponding tothe heating pin arrangement.

    ______________________________________                                        Key                                                                           ______________________________________                                                 1   Metering hopper                                                           2   Metering roll                                                             3   Lower chain belt                                                          4   Upper chain belt                                                          5   Gap                                                                       6   Pins                                                                      7   Lifting means                                                             8   Advancing device                                                          9   Synchronizing means                                                       10  Chain deflection point                                                    11  Chain deflection point                                           ______________________________________                                    

We claim:
 1. A method for making a thermoplastic foam productcomprising:piling a plurality of individual pieces of thermoplastic foammaterial having an average size of 15-30 mm to form a layer; compressingand compacting said layer of thermoplastic foam pieces; fusing togetherindividual thermoplastic foam pieces of the resultant compressed layerby perforating said layer using pins heated to a temperature of morethan 250° C.; and cooling the resultant perforated, fused layer.
 2. Aprocess for producing a layered material in sheet form from pieces ofthermoplastic foam having a softening temperature, comprising:piling aplurality of individual pieces of thermoplastic foam having an averagesize of 15-30 mm to form a piled-up layer of uniform height; compressingand compacting said layer of individual foam pieces at a temperaturebelow said softening temperature of said foam to form a compressed andcompacted layer; perforating said compressed and compacted layer ofthermoplastic foam whereby individual foam pieces are fused togetherusing pins heated to a temperature of more than 250° C., said pinshaving an outside diameter of 2 to 15 mm and an average spacing of 10 to50 mm, and with a dwell time of said pins within said compressed andcompacting layer of 1 to 10 seconds; and cooling the resultantperforated and fused layer while maintaining compression.
 3. A processaccording to claim 2, wherein said pieces of thermoplastic foam have anaverage apparent density of 30-150 kg/m³, and said piled-up layer formedby the piling of said pieces has a height of 20-200 mm.
 4. A processaccording to claim 3, wherein said piled-up layer formed by the pilingof said pieces has a height of 30-150 mm.
 5. A process according toclaim 1, wherein compression of the piled-up foam layer is performedcontinuously by means of a double-belt press, wherein each of the beltsare provided with perforations for guiding said pins.
 6. A processaccording to claim 5, wherein said pieces of thermoplastic foam arepiled on said double-belt press via a metering hopper.
 7. A processaccording to claim 2, wherein said pins have an outside diameter of3.5-4.5 mm, a surface temperature of 600°-700° C., and an averagespacing of 15-25 mm.
 8. A process according to claim 2, wherein saidpieces of thermoplastic foam are continuously piled to form saidpiled-up layer of uniform height.
 9. A process according to claim 2,further comprising providing a plastic membrane for smoothing thesurface of the perforated and fused layer.
 10. A process according toclaim 2, wherein said pins are heated to a temperature of up to 800° C.11. A process according to claim 2, wherein the dwell time of said pinsis 2-4 seconds.
 12. A process according to claim 2, wherein said piecesof thermoplastic foam are pieces of crosslinked polyethylene foam.
 13. Aprocess according to claim 2, wherein said pins are externally heated.14. A process according to claim 2, wherein said pins are internallyheated.
 15. A process according to claim 2, wherein the average apparentdensity of the pieces of thermoplastic foam is 30-140 kg/m³ and theapparent average density of the resultant layered material in sheet formis 120-196 kg/m³.
 16. A process according to claim 2, wherein said pinsare heated to a temperature of 400°-800° C.
 17. A process for producinga layered material in sheet form from pieces of thermoplastic foamhaving a softening temperature, comprising:piling a plurality ofindividual pieces of thermoplastic foam to form a piled-up layer ofuniform height; compressing and compacting said layer of individual foampieces at a temperature below said softening temperature of said foam toform a compressed and compacted layer; perforating said compressed andcompacted layer of thermoplastic foam whereby individual foam pieces arefused together using pins heated to a temperature of more than 250° C.,said pins having an outside diameter of 2 to 15 mm and an averagespacing of 10 to 50 mm, and with a dwell time of said pins within saidcompressed and compacted layer of 1 to 10 seconds; and cooling theresultant perforated and fused layer while maintaining compression;wherein compression of the piled-up foam layer is performed continuouslyby means of a double-belt press, in which each belt is provided withperforations for guiding said pins.